(1) Field of the Invention
This invention relates to improvements in attachment devices used to secure dental instruments in dental hand pieces. The invention is more particularly concerned with, but not limited to, a spiral spring clutch or chuck with the spiral spring housed within the bur tube, to permit the dental instrument to be inserted or removed therefrom. Whenever the instrument is rotated to unwind the spring, it releases the tool shank, but when the instrumemt is rotated to wind the spring, as when the cutting portion of the instrument engages a working surface, the spring grips the tool shank. The convolutions of the spring are initially in contact with each other, to prevent or minimize end play. The tool shank has a snug fit into the spring, to prevent it from falling out when there is no rotational force exerted by the dental instrument against the spring resistance. The invention is also concerned with means for holding the bur tube motionless when it is used with a turbine power system, so as to allow insertion and removal of the instrument from the bur tube when the turbine is not being powered by compressed air.
(2) Prior Art (Spring Clutch Handpiece)
In dental handpieces known to the prior art, spiral springs have been employed to grip the shank of a dental instrument in order for the instrument to rotate with some other component with which the spring was attached. This type of handpiece requires the spring to have both of its ends attached to other parts of the handpiece, so that these parts could be manually adjusted to grip or release a dental instrument shank which was manually inserted in or removed from the handpiece.
The present invention has advantages over that type of arrangement. It comprises a spring installed in the bore of an instrument tube, with one end of the spring lying free within the tube bore. No manual adjustment need be made to prepare the spring for the insertion or removal of the shank of the dental instrument, as the shank is inserted by simply rotating and pushing the shank into the spring, and removed by similarly rotating the shank and pulling it out of the spring. As there are no parts used to secure and to adjust the free end of the spring, manufacturing costs are also reduced.
Tool chucks employing a spring as a gripping device are found in non-analogous art, and furthermore do not provide the precision in rotation that is essential in the operation of a dental instrument. These devices rely on the spring itself to provide assistance in guiding or piloting the tool during its rotation which creates a wobbling effect not suitable for dental work, and also causes the wear of the spring. Such chucks also provide for either the fit of a tapered shank into a spring of uniform inside diameter, or the fit of a cylindrical or tapered shank into a spring with a tapered inside diameter. Consequently, these springs do not have uniform gripping strength along the shank, and may lose gripping power on the shank if the shank is moved downward in the spring, even though the shank body is still within the convolutions of the spring, The tapered nature of these chucks also makes it more difficult for the end of the shank to seat within the chuck and have a proper thrust bearing fit.
The present device employs a spiral spring to grip and retain the dental instrument, but does not employ the spring as a pilot to guide the rotation of the instrument, as the instrument fits snugly within two bores or bearings located at opposite ends of the instrument holder. During operation, these two bores prevent eccentric rotation and are machined so that the spring need not act as a pilot, which eliminates the wobbling effect that spring guidance manifests, and also reduces wear of the spring.
The spring in the present device is of uniform inside diameter, so that it may receive an instrument shank of uniform diameter. This allows the spring to grip the shank whenever part of the shank is within the spring convolutions. Consequently, the instrument holder has the additional safety factor of having the capacity to grip the instrument when, for whatever reason, the instrument shank is not completely inserted within the spring, thus preventing its inadvertent removal into the mouth of the patient. When the instrument is completely inserted, the uniform gripping power of the spring throughout its length around the shank provides for stronger retention than is provided by devices with either a tapered shank or a tapered spring. Also, because neither the shank or spring is tapered, the end of the shank is allowed to sit comfortably in the tube bore so as to have a proper thrust bearing fit.
Othr forms of the prior art employing a friction grip method of securing the dental instrument use a collet to secure the instrument. The collet is generally tubular in shape with slots in the tube which open at one end of the tube. This collet can sit in a cylindrical bore having a tapered end within the instrument holder, so that when a force is applied to the other end of the collet as by a threaded nut, the fingers of the collet formed between the slots will be pushed inwardly so as to grip a dental instrument which has been inserted in the instrument holder through the collet. The fingers of the collet are delicate and may be broken easily through shipping or through the use of the device. For example, if a dental instrument is not inserted in the instrument holder and the fingers of the collet are pushed inwardly, they can easily break because they are not met by the resistance of the instrument shank. An opening must be provided at the top of the head of the hand piece so that a wrench can be inserted through the head to tighten or loosen the collet. The collet also has a tendency to slip when the load on the dental instrument increases.
The present invention has advantages over the collet type instrument. It is not necessary to have an extra part such as a wrench to tighten or loosen the dental instrument. It also eliminates the necessity of having openings in the back part of the instrument head where bacteria and saliva can enter the hand piece, making it more aseptic. The problem with slipping is greatly reduced as the spring grip increases as the load on the dental instrument increases, and there is also little problem with the spring breaking through use.
In dental instrument employing turbines as a drive force, the prior art has used devices to allow for the removal of the dental instrument from the instrument tube. These prior art devices have openings in the top of the instrument head to allow for the inserting of a pin or wrench to effect removal of the instrument.
The present turbine operated arrangement device has a ramp type bearing which allows the instrument to be easily inserted in and withdrawn from the tube as it is not necessary to insert any separate component into the top of the dental head, and a more aseptic device is thus provided. Modifications of this device employ a lever pin or a locking pin housed within the instrument holder to hold the tube motionless to allow removal. Another modification employs a rubber bladder that can be pressurized so as to be forced against the turbine in order to hold the tube steady. These modifications also reduce the amount of bacteria that can enter the dental head, and are simple to operate.